Responses to mate loss by herring gulls Larus argentatus and great black-backed gulls Larus marinus

Late in incubation, 1 member of each of 41 incubating pairs was experimentally removed and its mate's response observed. All individuals either abandoned the initial clutch or brood. Only 1 individual replaced a lost mate that season. Males, however, abandoned their eggs significantly earlier than did females. Possible explanations for why males and females should react differently include cumulative reproductive effort, the tertiary sex ratio, the physical reserves of the deserted mate, the possibility and consequences of mixed reproductive strategies, and potential differences in replacement costs between the sexes due to differences in what each sex regards as its primary asset. -from Authors